Variables
FQL supports two kinds of variable declarations:
LET declares an immutable variable.VAR declares a mutable variable that can be reassigned later.
LET
The LET statement assigns the result of an expression to a variable.
The variable is introduced into the scope where the LET statement appears.
LET variableName = expression
After a variable is declared with LET, it cannot be reassigned.
LET a = [1, 2, 3] // initial assignment
a = PUSH(a, 4) // syntax error, unexpected identifier
LET a = PUSH(a, 4) // parsing error, variable 'a' is assigned multiple times
LET b = PUSH(a, 4) // allowed, result: [1, 2, 3, 4]
LET bindings often appear where a query needs to refer to an intermediate value, a subquery result, or another computed expression by name.
LET users = [
{
"id": 1,
"firstName": "Kikelia",
"lastName": "Coper",
"cart": [
{ "Name": "Garlic", "Price": "$7.46" },
{ "Name": "Flower - Commercial Spider", "Price": "$6.59" }
]
},
{
"id": 2,
"firstName": "Toni",
"lastName": "MacTeggart",
"cart": [
{ "Name": "Spice - Paprika", "Price": "$6.31" },
{ "Name": "Extract - Vanilla,artificial", "Price": "$4.74" },
{ "Name": "Wine - White, Cooking", "Price": "$1.50" },
{ "Name": "Nutmeg - Ground", "Price": "$1.30" }
]
},
{
"id": 3,
"firstName": "Neile",
"lastName": "Saice",
"cart": [
{ "Name": "Mustard Prepared", "Price": "$2.28" },
{ "Name": "Flower - Commercial Bronze", "Price": "$4.80" }
]
}
]
FOR u IN users
LET numProducts = LENGTH(u.cart)
RETURN {
"user": u,
"numProducts": numProducts,
"discount": numProducts >= 3
}
In this example, numProducts stores the number of items in the user’s cart. The value can then be reused in the returned object without calling LENGTH(u.cart) more than once.
LET is also useful for assigning the result of a subquery to a variable.
LET users = [
{ "id": 1, "name": "Moises Grisewood" },
{ "id": 2, "name": "Dell Marnes" },
{ "id": 3, "name": "Tobin Bilbery" },
{ "id": 4, "name": "Lorianne Posten" },
{ "id": 5, "name": "Drucill Cryer" }
]
LET friends = [
{ "id": 1, "name": "Maximo Massard", "userId": 1 },
{ "id": 2, "name": "Delainey Sancho", "userId": 1 },
{ "id": 3, "name": "Lindon Beale", "userId": 1 },
{ "id": 4, "name": "Gus Sprey", "userId": 3 },
{ "id": 5, "name": "Virgil Dallander", "userId": 3 },
{ "id": 6, "name": "Agretha Mackerel", "userId": 4 },
{ "id": 7, "name": "Christalle Aldins", "userId": 4 },
{ "id": 8, "name": "Karalynn Margery", "userId": 5 },
{ "id": 9, "name": "Rodolph Ladd", "userId": 5 },
{ "id": 10, "name": "Babette Brassill", "userId": 1 }
]
FOR u IN users
LET friends = (
FOR f IN friends
FILTER u.id == f.userId
RETURN f
)
RETURN { "user": u, "friends": friends, "numFriends": LENGTH(friends) }
Here, the inner FOR query finds the friends that belong to the current user. Assigning the result to friends makes the RETURN statement easier to read and allows the same value to be used more than once.
VAR
The VAR statement declares a mutable variable. Unlike variables declared with LET, variables declared with VAR can be reassigned.
The general syntax is:
VAR variableName = expression
A VAR variable can be updated later using assignment syntax:
VAR count = 0
count = count + 1
count = count + 1
RETURN count
VAR is suitable for values that change across multiple statements, such as counters, accumulators, or flags.
LET numbers = [1, 2, 3, 4, 5]
VAR total = 0
FOR n IN numbers
total = total + n
RETURN total
In this example, total starts at 0 and is updated for each value in numbers.